Verification of operational capability of a tape drive

ABSTRACT

Verification system logic operates PWM motor drivers for DC motors of a tape drive, and verifies the on time duty cycle period and offset of the PWM motor drivers; verifies DAC current reference and amplifier sense signals against thresholds; and verifies Hall sensor state sequence of the DC motors during rotation. If the verifications are successful, the logic rotates the DC motors, and, for each motor, verifies the time of acceleration at a desired torque; verifies a computed velocity based on a measured velocity to a reference velocity; and verifies an actual rotation rate to a computed velocity.

FIELD OF THE INVENTION

[0001] This invention relates to tape drives, and, more particularly, totape drives which employ DC motors, wherein the tape drive is formounting tape reels for rotation by the DC motors.

BACKGROUND OF THE INVENTION

[0002] Tape, such as magnetic tape, provides a means for physicallystoring data which may be archived or which may be stored in storageshelves of automated data storage libraries, and accessed when required.As an archival medium, tape often comprises the only copy of the data.

[0003] The tape is typically thin so as to maximize the length of a tapestored on a tape reel or reels, and thereby maximize the amount of datathat can be stored on the tape. If the tape drive does not functionproperly, the thin tape may be stretched or damaged, possibly causingloss of the data.

[0004] Tape drives frequently employ DC motors and feedback controlsystems with motor drivers for operating the DC motors, to produce wellcontrolled motion parameters such as position, velocity, and tapetension. Such control systems are usually very complex, and the feedbackcontrol system may compensate for marginal components, hiding latentproblems until a catastrophic failure occurs. At that point, if a user'stape is in the tape drive and under control of the feedback controlsystem, it is likely too late to protect the user's data.

SUMMARY OF THE INVENTION

[0005] In accordance with the present invention, a verification system,logic, and a method are provided for verifying operational capability ofa tape drive.

[0006] In one embodiment, logic is provided for operating a tape drive.The tape drive has a plurality of DC motors for rotating reels, aplurality of PWM motor drivers with DACs for operating the DC motors;and a plurality of Hall sensors for sensing the states of the DC motors.The logic operates the PWM motor drivers, and detects the Hall sensors.The logic:

[0007] operates the PWM motor drivers and verifies the on time dutycycle period and offset of the PWM motor drivers;

[0008] operates the PWM motor drivers in DISABLE mode and verifies DACcurrent reference and amplifier sense signals against positive andnegative thresholds; and

[0009] operates the PWM motor drivers to rotate the DC motors in atleast one direction, detecting the Hall sensors during the rotation, andverifies the Hall sensor state sequence of each of the DC motors forthat direction; and

[0010] if the verification of the on time duty cycle period and offsetfor the PWM motor drivers, the verification of the DAC current referenceand amplifier sense signals for the PWM motor drivers, and the Hallsensor state sequence for each of the DC motors, are all successful, thelogic operates the PWM motor drivers to rotate the DC motors; and

[0011] accelerates the DC motors with a desired torque, and verifies thetime of acceleration of each of the DC motors to a desired velocity;

[0012] verifies a computed velocity of each of the DC motors based on ameasured velocity, to a reference velocity; and

[0013] verifies an actual rotation rate of each of the DC motors to acomputed velocity thereof.

[0014] In another embodiment, additionally, upon detecting failure ofany of the verification operations, the logic provides an error signaland identifies which operation failed.

[0015] In still another embodiment, the logic conducts the operationswith the tape reels unmounted.

[0016] In a further embodiment, wherein the tape drive DC motors arebidirectional, the logic operates the PWM motor drivers to rotate the DCmotors in a forward direction and in a backward direction, detecting theHall sensors during the rotations, and verifies the Hall sensor statesequence of each of the DC motors for the forward direction and for thebackward direction. In another embodiment, the DC motors are rotatedsubsequent to the verification of the on time duty cycle period andoffset for the PWM motor drivers, and the verification of the DACcurrent reference and amplifier sense signals for the PWM motor drivers.

[0017] In a still further embodiment, the logic initially operates thePWM motor drivers in DISABLE mode, verifying PWM disable period, anddetermines the verification of the PWM on time duty cycle, and operatesthe PWM motor drivers in ENABLE mode, verifying PWM signal period anddetermines the verification of the offset.

[0018] For a fuller understanding of the present invention, referenceshould be made to the following detailed description taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a block diagrammatic illustration of a tape drive whichimplements the present invention;

[0020]FIG. 2 is a diagrammatic illustration of an example of testresults for the tape drive of FIG. 1 in accordance with the presentinvention;

[0021]FIGS. 3, 4 and 5 are flow charts depicting an embodiment of themethod of the present invention for verifying operational capability ofthe tape drive of FIG. 1; and

[0022]FIG. 6 is a diagrammatic illustration of Hall sensor signals formotion of a DC motor.

DETAILED DESCRIPTION OF THE INVENTION

[0023] This invention is described in preferred embodiments in thefollowing description with reference to the Figures, in which likenumbers represent the same or similar elements. While this invention isdescribed in terms of the best mode for achieving this invention'sobjectives, it will be appreciated by those skilled in the art thatvariations may be accomplished in view of these teachings withoutdeviating from the spirit or scope of the invention.

[0024] As discussed above, magnetic tape provides a means for physicallystoring data which may be archived or which may be stored in storageshelves of automated data storage libraries and accessed when required.FIG. 1 illustrates an example of a tape drive 10 which implements thepresent invention. A tape drive moves a tape, such as a magnetic tape,along a tape path 11, past at least one read/write head 12 which ispositioned at the tape path for reading and/or writing data with respectto the magnetic tape. The magnetic tape may be in the form of aremovable magnetic tape cartridge, and the cartridge may comprise alength of tape wound on a single reel, or on dual reels. An example of asingle reel tape drive is the IBM 3580 Ultrium magnetic tape drive basedon LTO (Linear Tape Open) technology. Another example of a single reeltape drive is the IBM 3590 Magstar magnetic tape drive and associatedmagnetic tape cartridge. An example of a dual reel tape drive is the IBM3570 magnetic tape drive and associated cartridge. In the case of asingle reel cartridge, the tape is unwound from the cartridge reel andwound onto a take-up reel of the tape drive. In the case of a dual reelcartridge, both the supply and take-up reels are in the cartridge. Thetape reels are mounted for rotation by a plurality of DC motors 15, 16which rotate the reels to move the tape longitudinally from one tapereel to another tape reel along the tape path 11. A digital signalprocessor or microprocessor controller 17 comprise the logic with aservo system 18, 19 for operating DC motors 15, 16 by means of a motorcontrol system 20, 21 to rotate the reels at velocities and withaccelerations that allow the tape to be moved at desired longitudinalspeeds as the tape is unwound from one tape reel and wound onto theother tape reel, while maintaining desired tension on the tape. Asdiscussed above, such servo and control systems may compensate formarginal components, hiding latent problems until a catastrophic failureoccurs.

[0025] The present invention verifies the proper function of theseparate components that make up the control system, before they areused in combination for the purpose of controlling the tape. Thus,components important to the invention do not include the tape, or theread/write head 12. A further motion servo input may comprise a servotrack or tracks recorded on the tape and read by the read/write head 12and decoded by a servo decoder 18. Alternatively, servo tachometers maybe provided at each DC motor or reel to determine the reel rotationalvelocities. Further, a servo tachometer may be provided in the tape path11 to directly measure the tape velocity. No direct input of the tapevelocity is employed in the present invention, which is applied to thetape drive 10 before the tape is mounted in the tape drive.

[0026] The tape reels are driven by DC motors 15, 16, for example,comprising brushless DC motors, but the present technique is alsoapplicable to brushed DC motors. The DC motors are driven by PWM motordriver control systems 20, 21 with current-mode or transconductanceamplifiers, as is known to those of skill in the art. The amplifiershave current sense circuits which produce a motor current signal that issubtracted from a reference current supplied by a DAC (digital to analogconvertor). The difference between the current reference and the currentsense produces an error current signal that is amplified and filtered ina compensator circuit that produces a motor control signal. This signaldrives a pulse width modulator (PWM) which produces a digital signalthat continually reverses the polarity of the voltage that is applied tothe DC motor. The PWM signal is fed to a commutator circuit which isalso controlled by commutation sensors (Hall sensors) 25, 26 that sensethe motor armature position and select the proper motor winding that isto be excited.

[0027] The PWM signal is also fed to the servo control logic 19 thatmeasures the on period (duty cycle) and the total period of the PWMsignal. This information is used in the servo control system to computethe motor angular velocities, which velocities are employed in thepresent invention.

[0028] In the servo system, the tape longitudinal velocity is computedfrom the motor angular velocities, and/or is measured from tachometers,and is used as feedback information in the tape servo control system.The servo and control system 19, 20, 21 is a multiple input, multipleoutput (MIMO) system that computes two control values for the plant,which is made up of the two motors 15, 16, two tape reels, and the tapepath connecting the two reels. This is so that the reels are rotated atthe appropriate, usually different, rotational velocities, such that thetape is moved from one tape reel having one diameter of tape, to anothertape reel having another diameter of tape, at the same longitudinalvelocity.

[0029] The MIMO control system computes the control values, in this casethe required motor currents, to achieve the desired tape motionparameters. The computed motor currents are converted to analog voltagesin digital to analog convertors (DACs) which drive the current modeamplifiers.

[0030] In the present invention, components of the system are verifiedfor function individually prior to use in the integrated control system.Important parameters of each component are measured and compared toacceptable limits for verification. If the measured parameter is outsideacceptable limits, the verification system flags the component asdefective, and provides an error signal. The verification system maypresent the results of the verification process in summary form at theconclusion of a test, along with the parameter measurements, such as isillustrated in FIG. 2. In FIG. 2, all the parameter measurements areprovided along with a pass-fail flag for each measurement.

[0031] The verification process of the present invention is run on thehardware, for example, after the machine power on step. It may also beinvoked during special error analysis steps when machine functions areto be verified. During the manufacturing phase of the tape drive, thisverification process will assure that functional components have beenassembled into every tape drive produced.

[0032] In accordance with an aspect of the present invention, when afailing component is detected, the verification process identifies thefailing component, and provides the data for the failure, thus isolatingthe component that must be replaced to correct failure of the tapedrive.

[0033] Further, in the customer environment, the verification process ofthe present invention detects failing components at machine power on,and provides status of the failure that will prevent usage of themachine, preventing jeopardy to customer data.

[0034] Referring additionally to FIG. 3, the verification process checksout the hardware system in a systematic manner, beginning with circuitsand hardware that are checked without rotating the DC motors, and, ifverified, the motors are then rotated and accelerated. In accordancewith one aspect of the present invention, the verification process isconducted with tape reels unmounted, thereby assuring that damage to atape is avoided.

[0035] Beginning at step 100, for example, comprising a power on of thetape drive, the digital signal processor or microprocessor controller 17logic conducts the component verification process. For example, theprocess begins in step 101 with an optional initial step of operatingthe PWM motor drivers in DISABLE mode, such that the DC motors aredisabled, and measuring the PWM disable period and on time duty cycle.At power on, the motor driver power amplifiers are biased with a powervoltage, such as +12 volts, and are in the disabled mode, as is known tothose of skill in the art. In this mode, the PWM signals will be activewith approximately a 50% duty cycle. The first tests are to verify thePWM signals are working in this manner, and at the correct frequencies.This step may be omitted and, if faulty, the result would appearimmediately in a following test. Thus, in step 101, the PWM disableperiod for each motor driver amplifier is measured, and, in step 102,the PWM disable period is verified, thereby verifying that the motordriver amplifier is functioning, in that the PWM oscillators areworking, and at the correct frequency. Also in step 101, the PWM signalon time is measured, and, step 102 verifies whether the PWM disabled ontime duty cycle is proper.

[0036] If the PWM disable period or on time duty cycle is outside adesired threshold level, the process proceeds to connector 104, whichwill indicate component failure, as will be discussed.

[0037] Successful verification of the PWM disable period and on timeduty cycle are illustrated in the table of FIG. 2.

[0038] Then, in step 108 of FIG. 3, the enable signal to the motordriver amplifiers is activated with a value of zero written to thedigital to analog convertors (DACs). In this mode, the PWM signal isagain measured, and the difference between the on time and 50% of theperiod is computed to give the PWM offset measurement. If steps 101 and102 were omitted, the on time measurement is estimated, any failure ofthe PWM signals will also be identified at this point. Thus, the PWMmotor drivers are operated in ENABLE mode in step 108, and step 109verifies the enable on time duty cycle period and offset of the PWMmotor drivers. The PWM offset is the difference between the PWM on time(time when the PWM signal is in the “HI” binary state) and one half ofthe PWM period (time for one full cycle of PWM). The PWM on time, forzero current command to the DC motors, should be 50% of the period time,so the PWM offset of zero is good, and the PWM offset is verified if itis within a +/− tolerance of zero.

[0039] Again, if the enable on time duty cycle period and/or offset of aPWM motor driver is outside a desired threshold level, the processproceeds to connector 104, which will indicate component failure, aswill be discussed.

[0040] Successful verification of the enable on time duty cycle periodand offset of the PWM motor drivers are illustrated in the table of FIG.2.

[0041] In step 112 of FIG. 3, the amplifier enable signal isdeactivated, and the motor driver error positive and negative thresholdsare measured. With the amplifiers in the disabled state, the amplifiersproduce no current in the motors, and the current sense amplifiers willremain with a zero output signal. An amplifier error detection circuitsums these two voltages and monitors the difference between the currentreference and the current sense signals, as is known to those of skillin the art. When an error threshold is exceeded, a digital signal isgenerated which the digital signal processor or microprocessorcontroller 17 logic of FIG. 1 can monitor. In step 112 of FIG. 3, withthe amplifier in disable mode, this circuit detects a difference betweenthese signals which is interpreted as a failure condition for theamplifier, if the amplifier were in enable mode. This failure conditionis set when the difference between the reference current and sensecurrent exceed a predetermined threshold. In accordance with the presentinvention, this threshold is measured by monitoring the error signalwhich is provided to the digital signal processor or microprocessorcontroller logic, while various values are written to the DACs. When theDAC value is large enough, the errors are set, and this DAC valuerepresents the error threshold for the motor driver amplifier. In oneexample, the DACs are written in a binary converging technique to findthe error threshold beginning with the most significant bit of the DACand working to the least significant bit. In step 114, the errorthresholds are stored by the logic, and step 115 verifies whether thethresholds are OK. If the thresholds are not OK, the process proceeds toconnector 104, which will indicate component failure, as will bediscussed.

[0042] Successful verification of the thresholds are illustrated in thetable of FIG. 2.

[0043] As is known to those of skill in the art, the two DAC voltages ofthe two reel motor driver systems are summed together and compared to apredetermined analog threshold. When the threshold is exceeded, adigital signal is generated which the logic can monitor. In one example,the DACs provide an analog current reference signal to the motor poweramplifiers. The amplifiers apply voltage to the motor windings tocontrol the motor current to the reference from the DACs. The amplifiershave “current sense” circuits to do this, the current sense circuitsprovide an analog signal representing the actual current flowing in theDC motors. The difference between the DAC reference and the currentsense signals is monitored in an “amplifier error checking” circuit,and, if these two signals don't agree within the “threshold” tolerance,the error checking circuit generates a binary signal to the logicindicating this condition. In step 117 of FIG. 3, the two DACs arewritten with the same magnitude values, but with opposite signs, thusone DAC will be positive polarity and the other DAC will be negativepolarity. In this case, the sum of the two DAC values will be zero, andthe analog threshold should not be exceeded, regardless of the magnitudevalues written to the DACs. If the analog threshold is exceeded, this isan indication that one of the DACs has failed. In this verificationstep, all DAC values from the largest negative value to the largestpositive value may be written to the DACs, and the error condition ismonitored.

[0044] Step 119 verifies whether the error threshold was activated. Ifthe error threshold was activated, the process proceeds to connector104, which will indicate component failure, as will be discussed.

[0045] Successful verification of the error threshold is illustrated inthe table of FIG. 2.

[0046] Thus, steps 112, 114, 115, 117, 119 of FIG. 3 illustrate anembodiment of the present invention for operating the PWM motor driversin DISABLE mode and verifying DAC current reference and amplifier sensesignals against positive and negative thresholds.

[0047] Step 119 then leads to connector 125 and to step 130 of FIG. 4.Preferably, but not necessarily, steps 101 to 119 of FIG. 3 arecompleted prior to step 130 so that the operation of the PWM motordrivers 20 and 21 of FIG. 1 are verified without any motion of the ofthe components of the servo control system. This constitutes the staticcomponent test of the control system. Thus, if all the previous testshave passed, the verification process proceeds to a test of thecomponents involving operation of the motor drivers for rotating the DCmotors.

[0048] In step 130 of FIG. 4, the DC motors are rotated in at least onedirection. The DC motors are typically bidirectional to move the tape ineither direction. Optionally, the DC motors may be first rotated in onedirection, and then rotated in the opposite direction. The illustratedexample of FIG. 4 rotates the DC motors first in the forward direction,and then rotates the DC motors in the backward direction.

[0049] In step 130 of FIG. 4, the first test is a forward motion test ofthe DC motors, monitoring the Hall sensors 25, 26 of FIG. 1. An optionalextra test may comprise rotating the motors at a fixed velocity andcounting the Hall count change during a predetermined time period. Thetime measurement may be made using counters of the servo logic, and theresult is compared to pass-fail thresholds for high and low values. Anexample of a rotate forward count is illustrated in the table of FIG. 2.

[0050] In step 130 of FIG. 4, while the DC motors are rotating in theforward direction, and after the optional forward rotation test hascompleted, the Hall sensor forward motion state verification isconducted. In this test, there is a test for invalid Hall transitionsand a concurrent test for valid Hall sequence for forward rotation. Asis known to those of skill in the art, as a DC motor is rotating, theHall states proceed through a specific sequence. For example, referringto FIG. 6, the sequence of states for a three channel Hall sensor areindicated while the motor is rotated in one direction, for example, theforward direction. The sequence of states for this direction of motionis 4, 5, 1, 3, 2, 6.

[0051] During step 130 of verification of FIG. 4, the sequence ofexpected Hall states is monitored, and, during which time, theoccurrence of an unexpected Hall state will force an error detection.For example, referring to FIG. 6, in state 4, the logic looks for state6 to occur, which happens after 5 Hall states pass (5, 1, 3, 2, 6), and,in state 6, the next state the logic looks for is 2. That requiresanother 5 Hall transitions to occur (4, 5, 1, 3, 2). This continuesuntil the logic finally searches for state 5. In all, 25 Hall statesshould pass for this test to complete, so that the pass-fail Hall countwill be 25 to pass, any other number will fail. In the example, the testcauses the motor to rotate through at least one full rotation, sincethere are 24 Hall states per full motor turn, thereby checking all themagnetic poles in the motor with the Hall sensors. Another set of logicchecks to make sure that the Hall sequence is always 4, 5, 1, 3, 2, 6,for the whole test duration, and if the Hall sequence is different thanthat, the test fails.

[0052] If, in step 131, both the tests for invalid Hall transitions andthe concurrent test for valid Hall sequence for forward rotation aremet, this verification of the Hall sensor state sequence of each of saidDC motors for at least one direction passes. If either of the testsfails, the process proceeds to connector 104, which will indicatecomponent failure, as will be discussed.

[0053] Successful verification of the Hall sensor state sequence formotion in the forward direction is illustrated in the table of FIG. 2.

[0054] The optional backward motion motor rotation test 133 of FIG. 4,may additionally comprise the optional extra test of rotating the motorsat a fixed velocity and counting the Hall count change during apredetermined time period, comparing the result to pass-fail thresholdsfor high and low values, as discussed above for the forward direction.An example of a rotate backward count is illustrated in the table ofFIG. 2.

[0055] The backward motion state verification test is then conducted instep 133 of FIG. 4. As discussed above, there is a test for invalid Halltransitions and a concurrent test for valid Hall sequence states forbackward rotation. During this step of verification, the sequence ofexpected Hall states is monitored, during which time, the occurrence ofan unexpected Hall state will force an error detection. If, in step 135,both of these conditions are met, this test passes. Once again, whenthis test begins, the expected sequence of Hall transitions ismonitored, but for the opposite direction of rotation. Since the nextsequential backward state will not occur until five Hall states haveoccurred, the total number of states in the test sequence is (6−1)×5=25.This number is monitored at the end of the test as a pass-faildetermination of the proper occurrence of Hall states for five cycles ofthe Hall sensors of the motors.

[0056] If, in step 135, both the tests for invalid Hall transitions andthe concurrent test for valid Hall sequence for backward rotation aremet, this verification of the Hall sensor state sequence of each of saidDC motors for the backward direction passes. If either of the testsfails, the process proceeds to connector 104, which will indicatecomponent failure, as will be discussed.

[0057] Successful verification of the Hall sensor state sequence formotion in the backward direction is illustrated in the table of FIG. 2.

[0058] In accordance with the present invention, if the previous testshave completed successfully, there is sufficient function for motion ofthe DC motors to be controlled and monitored.

[0059] Thus, in steps 140 and 141 of FIG. 4, tests of motor controlparameters are begun. As one example, the next test performed is themotor acceleration test. The acceleration test is preferably, but notnecessarily, begun from a stopped condition. Thus, step 140 comprisesbringing the motors to a stop condition by disabling the amplifiers anddynamic braking of the motors.

[0060] During the test of step 141, the motors are driven with apredetermined fixed torque value. The torque may be the same, ordifferent, for each of the DC motors. The constant torque value isdeveloped by writing a fixed value to the DACs with the motors enabled.With the fixed value of torque applied, the DC motors will accelerate ata rate determined by the torque value, and the inertia's of the motorsand their loads, and by friction. The time duration of acceleration andthe motor velocity are monitored to determine the elapsed time to reacha desired velocity. The elapsed time for this acceleration is measuredand, in step 145, compared to pass-fail criteria.

[0061] If the step 145 verification of time of acceleration of each ofthe DC motors to a desired velocity fails, the process proceeds toconnector 104, which will indicate component failure, as will bediscussed.

[0062] Successful verification of the time of acceleration of each ofthe DC motors is illustrated in the table of FIG. 2.

[0063] Step 145 then leads to connector 150 and to step 155 of FIG. 5,which is a DC motor velocity test. This test determines if the measuredand computed motor velocity conforms to a reference velocity when themeasured velocity is used in the feedback control system for each motor.The velocities may be the same, or different, for each of the DC motors.In the test, the reference velocity is maintained for a long enoughduration to allow the motor velocities to stabilize at a steady state.After this time duration, the value of the measured velocity isdetermined and compared, in step 156, to the reference velocity. Thepass-fail criteria for this test is determined by comparing the measuredmotor velocity to the reference velocity within an allowed threshold.

[0064] If the step 156 verification of computed velocity of each of theDC motors based on a measured velocity, to a reference velocity fails,the process proceeds to step 157, which will indicate component failure,as will be discussed.

[0065] Successful verification of the computed velocity of each of theDC motors based on a measured velocity, to a reference velocity isillustrated in the table of FIG. 2.

[0066] The process proceeds at step 160 of FIG. 5 which verifies whetherthe actual motor velocity and the computed motor velocity agree towithin a required tolerance. As is known to those of skill in the art,the computed motor velocity is used to compute secondary velocity of thetape for feedback in the tape transport. The test of step 160 providesverification that the computed value of motor velocity based on the PWMsignals represents the actual value of motor velocity. Alternatively,other examples of computed motor velocity may comprise velocitiescalculated from tachometers that may be provided at each DC motor orreel to determine the reel rotational velocities. However, no servotachometer provided in the tape path is measured, in that theverification is conducted before the tape is mounted in the tape drive.The velocities may be the same, or different, for each of the DC motors,and may be the same, or different, than velocities of other verificationsteps.

[0067] In step 160, the actual motor velocity is calculated from thefull rotation time of the motor, measured by monitoring the timeduration of 24 Hall states. The test is done with the DC motor velocityof each of the DC motors controlled to a stable velocity, and step 161verifies whether the actual rotation rate of each of the DC motors isequal to a computed velocity thereof, within a predetermined tolerance.

[0068] If the step 161 verification of the actual rotation rate of eachof the DC motors to a computed velocity thereof fails, the processproceeds to step 157, which will indicate component failure, as will bediscussed.

[0069] Connectors 104 of FIGS. 3, 4, and 5 also lead to step 157 of FIG.5.

[0070] Successful verification of the actual rotation rate of each ofthe DC motors to a computed velocity is illustrated in the table of FIG.2.

[0071] As the last illustrated verification step, step 161 of FIG. 5, ifsuccessful, also proceeds to step 157.

[0072] Connectors 104 of FIGS. 3, 4, and 5 also lead to step 157 of FIG.5.

[0073] In step 157, the verification system logic, upon detectingfailure of any of the operations, provides an error signal andidentifies the operation that failed.

[0074] The table of FIG. 2 may be provided in step 157 of FIG. 5, andpresents the results of all the motor and motor driver system componentswhose operation has been verified. In the example of FIG. 2, the dataand pass-fail flags are shown for both DC motors, called “inboard” and“outboard” motors, and for the driver circuits of the tape drive. If thevalue returned for the result for all tests is “1”, then all componentsof the test have passed. Any test with a result of “2” indicates thatcomponent failed it's test. A result value of “0” indicates the test forthat component could not be completed, due to failure of an earliercomponent test. In the example, all tests are shown as successful.

[0075] The precise sequencing of the verification tests may be altered,as is known to those of skill in the art, although the tests comprisingsteps 100-135 of FIGS. 3 and 4 must be successfully completed, such thatif verification of the on time duty cycle period and offset for the PWMmotor drivers, the verification of the DAC current reference andamplifier sense signals for the PWM motor drivers, and the Hall sensorstate sequence for each of the DC motors, are all successful, then thePWM motor drivers may be operated to rotate the DC motors for theacceleration and velocity verification tests.

[0076] While the preferred embodiments of the present invention havebeen illustrated in detail, it should be apparent that modifications andadaptations to those embodiments may occur to one skilled in the artwithout departing from the scope of the present invention as set forthin the following claims.

I claim:
 1. A verification system for a tape drive, said tape drivehaving a plurality of DC motors, said verification system comprising: aplurality of PWM motor drivers with DACs for operating said DC motors; aplurality of Hall sensors for sensing the states of said DC motors; andlogic for operating said PWM motor drivers, and detecting said Hallsensors, said logic: operating said PWM motor drivers and verifying theon time duty cycle period and offset of said PWM motor drivers;operating said PWM motor drivers in DISABLE mode and verifying DACcurrent reference and amplifier sense signals against positive andnegative thresholds; and operating said PWM motor drivers to rotate saidDC motors in at least one direction, detecting said Hall sensors duringsaid rotation, and verifying the Hall sensor state sequence of each ofsaid DC motors for said at least one direction; and if said verificationof said on time duty cycle period and offset for said PWM motor drivers,said verification of said DAC current reference and amplifier sensesignals for said PWM motor drivers, and said Hall sensor state sequencefor each of said DC motors, are all successful, operating said PWM motordrivers to rotate said DC motors; and accelerating said DC motors atdesired torque, verifying time of acceleration of each of said DC motorsto a desired velocity; verifying a computed velocity of each of said DCmotors based on a measured velocity, to a reference velocity; andverifying an actual rotation rate of each of said DC motors to acomputed velocity thereof.
 2. The verification system of claim 1,wherein said logic, upon detecting failure of any of said operations,provides an error signal and identifies the operation that failed. 3.The verification system of claim 2, wherein said tape drive is formounting tape reels for rotation by said plurality of DC motors, andsaid operations are conducted with said tape reels unmounted.
 4. Theverification system of claim 1, wherein said DC motors arebidirectional, and wherein said logic operates said PWM motor drivers torotate said DC motors in a forward direction and in a backwarddirection, detecting said Hall sensors during said rotations, andverifying the Hall sensor state sequence of each of said DC motors forsaid forward direction and for said backward direction.
 5. Theverification system of claim 4, wherein said logic rotates said DCmotors subsequent to said verification of said on time duty cycle periodand offset for said PWM motor drivers, and said verification of said DACcurrent reference and amplifier sense signals for said PWM motordrivers.
 6. The verification system of claim 1, wherein said logicadditionally initially operates said PWM motor drivers in DISABLE mode,verifying PWM disable period, and determining said verification of saidPWM on time duty cycle, and operates said PWM motor drivers in ENABLEmode, verifying PWM signal period and determining said verification ofsaid offset.
 7. Logic for operating a tape drive, said tape drive havinga plurality of DC motors for rotating reels, a plurality of PWM motordrivers with DACs for operating said DC motors, a plurality of Hallsensors for sensing the states of said DC motors, said logic foroperating said PWM motor drivers, and detecting said Hall sensors, saidlogic: operating said PWM motor drivers and verifying the on time dutycycle period and offset of said PWM motor drivers; operating said PWMmotor drivers in DISABLE mode and verifying DAC current reference andamplifier sense signals against positive and negative thresholds; andoperating said PWM motor drivers to rotate said DC motors in at leastone direction, detecting said Hall sensors during said rotation, andverifying the Hall sensor state sequence of each of said DC motors forsaid at least one direction; and if said verification of said on timeduty cycle period and offset for said PWM motor drivers, saidverification of said DAC current reference and amplifier sense signalsfor said PWM motor drivers, and said Hall sensor state sequence for eachof said DC motors, are all successful, operating said PWM motor driversto rotate said DC motors; and accelerating said DC motors with desiredtorque, verifying time of acceleration of each of said DC motors to adesired velocity; verifying a computed velocity of each of said DCmotors based on a measured velocity, to a reference velocity; andverifying an actual rotation rate of each of said DC motors to acomputed velocity thereof.
 8. The logic of claim 7, additionally, upondetecting failure of any of said operations, provides an error signaland identifies which operation failed.
 9. The logic of claim 8, whereinsaid tape drive is for mounting tape reels for rotation by saidplurality of DC motors, and wherein said logic conducts said operationswith said tape reels unmounted.
 10. The logic of claim 7, wherein saidtape drive DC motors are bidirectional, and wherein said logic operatessaid PWM motor drivers to rotate said DC motors in a forward directionand in a backward direction, detecting said Hall sensors during saidrotations, and verifying the Hall sensor state sequence of each of saidDC motors for said forward direction and for said backward direction.11. The logic of claim 10, wherein said logic rotates said DC motorssubsequent to said verification of said on time duty cycle period andoffset for said PWM motor drivers, and said verification of said DACcurrent reference and amplifier sense signals for said PWM motordrivers.
 12. The logic of claim 7, initially operating said PWM motordrivers in DISABLE mode, verifying PWM disable period, and determiningsaid verification of said PWM on time duty cycle, and operating said PWMmotor drivers in ENABLE mode, verifying PWM signal period anddetermining said verification of said offset.
 13. A magnetic tape drivefor reading and/or writing data with respect to magnetic tape,comprising: at least one read/write head positioned at a tape path forreading and/or writing data with respect to a magnetic tape in said tapepath; a plurality of DC motors, whereby tape reels mounted for rotationby said plurality of DC motors, provide said magnetic tape to be movedlongitudinally from one said tape reel to another said tape reel alongsaid tape path; a plurality of PWM motor drivers with DACs for operatingsaid DC motors; a plurality of Hall sensors for sensing the states ofsaid DC motors; and logic for operating said PWM motor drivers, anddetecting said Hall sensors, said logic: operating said PWM motordrivers and verifying the on time duty cycle period and offset of saidPWM motor drivers; operating said PWM motor drivers in DISABLE mode andverifying DAC current reference and amplifier sense signals againstpositive and negative thresholds; and operating said PWM motor driversto rotate said DC motors in at least one direction, detecting said Hallsensors during said rotation, and verifying the Hall sensor statesequence of each of said DC motors for said at least one direction; andif said verification of said on time duty cycle period and offset forsaid PWM motor drivers, said verification of said DAC current referenceand amplifier sense signals for said PWM motor drivers, and said Hallsensor state sequence for each of said DC motors, are all successful,operating said PWM motor drivers to rotate said DC motors; andaccelerating said DC motors with desired torque, verifying time ofacceleration of each of said DC motors to a desired velocity; verifyinga computed velocity of each of said DC motors based on a measuredvelocity, to a reference velocity; and verifying an actual rotation rateof each of said DC motors to a computed velocity thereof.
 14. Themagnetic tape drive of claim 13, wherein said logic, upon detectingfailure of any of said operations, provides an error signal andidentifies the operation that failed.
 15. The magnetic tape drive ofclaim 14, wherein said operations are conducted with said tape reelsunmounted.
 16. The magnetic tape drive of claim 13, wherein said DCmotors are bidirectional, and wherein said logic operates said PWM motordrivers to rotate said DC motors in a forward direction and in abackward direction, detecting said Hall sensors during said rotations,and verifying the Hall sensor state sequence of each of said DC motorsfor said forward direction and for said backward direction.
 17. Themagnetic tape drive of claim 16, wherein said logic rotates said DCmotors subsequent to said verification of said on time duty cycle periodand offset for said PWM motor drivers, and said verification of said DACcurrent reference and amplifier sense signals for said PWM motordrivers.
 18. The magnetic tape drive of claim 13, wherein said logicadditionally initially operates said PWM motor drivers in DISABLE mode,verifying PWM disable period, and determining said verification of saidPWM on time duty cycle, and operates said PWM motor drivers in ENABLEmode, verifying PWM signal period and determining said verification ofsaid offset.
 19. A method for verifying operational capability of a tapedrive, said tape drive having a plurality of DC motors for rotatingreels, a plurality of PWM motor drivers with DACs for operating said DCmotors, a plurality of Hall sensors for sensing the states of said DCmotors, said logic for operating said PWM motor drivers, and detectingsaid Hall sensors, said method comprising the steps of: operating saidPWM motor drivers and verifying the on time duty cycle period and offsetof said PWM motor drivers; operating said PWM motor drivers in DISABLEmode and verifying DAC current reference and amplifier sense signalsagainst positive and negative thresholds; and operating said PWM motordrivers to rotate said DC motors in at least one direction, detectingsaid Hall sensors during said rotation, and verifying the Hall sensorstate sequence of each of said DC motors for said at least onedirection; and if said verification of said on time duty cycle periodand offset for said PWM motor drivers, said verification of said DACcurrent reference and amplifier sense signals for said PWM motordrivers, and said Hall sensor state sequence for each of said DC motors,are all successful, operating said PWM motor drivers to rotate said DCmotors; and accelerating said DC motors with desired torque, verifyingtime of acceleration of each of said DC motors to a desired velocity;verifying a computed velocity of each of said DC motors based on ameasured velocity, to a reference velocity; and verifying an actualrotation rate of each of said DC motors to a computed velocity thereof.20. The method of claim 19, additionally comprising the step of: upondetecting failure of any of said operation steps, providing an errorsignal and identifying which operation failed.
 21. The method of claim20, wherein said tape drive is for mounting tape reels for rotation bysaid plurality of DC motors, and said method comprises conducting saidoperation steps with said tape reels unmounted.
 22. The method of claim19, wherein said tape drive DC motors are bidirectional, and whereinsaid step of operating said PWM motor drivers to rotate said DC motorscomprises: operating said PWM motor drivers to rotate said DC motors ina forward direction and in a backward direction, detecting said Hallsensors during said rotations, and verifying the Hall sensor statesequence of each of said DC motors for said forward direction and forsaid backward direction.
 23. The method of claim 22, wherein said stepof operating said PWM motor drivers to rotate said DC motors isconducted subsequent to said verification of said on time duty cycleperiod and offset for said PWM motor drivers, and said verification ofsaid DAC current reference and amplifier sense signals for said PWMmotor drivers.
 24. The method of claim 19, comprising the initial stepsof operating said PWM motor drivers in DISABLE mode, verifying PWMdisable period, and determining said verification of said PWM on timeduty cycle, and operating said PWM motor drivers in ENABLE mode,verifying PWM signal period and determining said verification of saidoffset.